1. Field
One or more exemplary embodiments relate to a golf ball, and more particularly, to a golf ball which has a superior straight flight feature and an increased flight time upon being hit by controlling the shapes of the dimples formed in a surface of the golf ball so that a flight distance and flight stability may be greatly improved.
2. Description of the Related Art
Dimples in a surface of a golf ball directly affect aerodynamic flight of the golf ball.
When the golf ball is hit using a golf club, the golf ball starts to fly due to a strong repulsive elasticity generated from the core of the golf ball and simultaneously a backspin of the golf ball is generated according to a loft angle of the golf club. A trajectory of the golf ball in flight has a different form according to various specifications of the golf ball.
Even when initial trajectories are similar to one another, the shape of a trajectory, the apex of a trajectory, flight time, etc. may greatly vary according to the type, shape or arrangement of the dimples. Also, even when the same golfer hits the golf ball by using the same golf club, the flight characteristics of the golf ball vary according to the differences in repulsive elasticity, rigidness, and spin performance of the golf ball. Particularly, duration of flight, the height of an apex, straightness of flight, effects of wind, etc. greatly vary according to the shape, size, number, size ratio, depth, arrangement method, etc. of the dimples.
In general, the most used dimple shape of a golf ball is a circular dimple. The circular dimple is most widely used because it easily maintains a constant air flow and enables a balanced arrangement over an overall surface of the golf ball. Also, since manufacturing of a mold cavity is easy, the circular dimple is applied to many golf balls. In regard to the circular dimple, however, flight performance of a golf ball greatly varies according to the size of the dimple. For a relatively small circular dimple, it may be difficult to get lift but a wind effect may be lower and thus more stable flight may be possible. In contrast, for a relatively large circular dimple, it may be easy to get lift but the wind effect may be higher and thus flight may be less stable. Accordingly, the golf ball may fly in an unintended direction toward an unintended destination. Also, when putting a golf ball, in the case of a large dimple, since there is a difference between when a surface of a putter contacts a land surface where no dimple is formed and when the surface of a putter directly contacts a surface of a dimple, directional consistency may not be guaranteed. In particular, the difference may increase further when short distance putting is performed. To overcome the above problem, every effort has been made by many people.
U.S. Pat. No. 5,879,245 discloses that neighboring dimples in a surface of a sphere divided into a spherical polyhedron are connected via air connection channels so that independence of each dimple is reduced, providing continuity in a flow of air, and thus the drag generated during flight of a golf ball is reduced and the flight stability and the flight distance are increased. However, since the surface of a golf ball having much unevenness due to the connection channels may be easily damaged during hitting by a short iron or wedge, the durability of the golf ball may be reduced.
U.S. Pat. No. 5,957,787 discloses that a surface of a sphere is divided into 20 spherical surfaces, the largest circular dimples are arranged at a center area of each spherical triangle, and an annular dimple having the same center as the circular dimple is arranged outside the circular dimple so that a drag coefficient in a low-speed area may be lowered and rotation may be maintained relatively longer when the annular dimple is disposed in a direction perpendicular to an air flow direction, thereby providing the flight stability and increasing the flight distance. However, due to an annular concave surface having one large continuous depth, a flow of air in the annular dimple becomes strong so that an initial trajectory may be excessively lowered and thus an increase in the flight distance with an appropriate trajectory may be difficult to achieve.
U.S. Pat. No. 6,709,349 discloses that, in arrangement of the dimples in a surface of a golf ball, radial arms in various shapes including a concave surface or a protruding portion are radially formed from a center of a dimple or a position almost close to the center, or radial arms in a uniform shape from a hub to an edge at the center of a dimple, and sub-dimples in various shapes are formed in an edge portion of a dimple or inside the dimple, thereby increasing the flight distance by agitating the flow of air to quickly convert the flow energy of air into flying energy of a golf ball. However, in '349 patent, since the sub-dimples are formed symmetrically in each dimple area relative to a center of each dimple, and the entire portion of the inside of one dimple receives the same pressure at any position thereof, not helping a rotational force, but increasing pressure drag and frictional drag of a golf ball, thereby decreasing the flight distance due to a rapid change in a trajectory during flight.
U.S. Patent Publication No. 2012/0302377 A1 discloses that elliptical or non-circular dimples are arranged in a surface of a golf ball having a spherical polyhedron shape, and the dimples have a non-circular shape which has a major axis of a length at least 1.2 times greater than that of a minor axis thereof, are each composed of a pair of circular arcs, and have a depth which causes the peripheral edges of the dimples to generate turbulence so that a separation width at a separation boundary may be reduced to a level less than that of a golf ball having circular dimples and thus the drag during flight of a golf ball may be decreased while increasing the flight distance. However, since there is a large difference between the major axis and the minor axis in the dimples having the above shape, if the same portion of a golf ball is not repeatedly hit during hitting, flight directions differ when a major axis side is hit or a minor axis side is hit so that flight stability may be seriously reduced.
In a general circular dimple, when the size of a dimple is equal to or greater than 0.19 inch, it is easy to get lift but wind effect may be increased during flight so that flight stability becomes poor. In contrast, when the size of a dimple is equal to or less than 0.14 inch, it is easy to achieve flight stability but it may be difficult to get lift so that the flight distance may be relatively short. Also, when putting, a difference is generated between when a relatively large dimple contacts a putter surface and when a relatively small dimple contacts the putter surface, in the case of the relatively large dimple, the golf ball may roll in a direction that is different from an intended direction within a short distance.